Recently, in a semiconductor manufacturing process, further improvement in a microfabrication technique has been required along with an increase in element integration density and performance. In the semiconductor manufacturing process, an etching technique is one of the important microfabrication techniques. Recently, among the etching techniques, a plasma etching technique capable of microfabrication on a large area with high efficiency has been mainly used.
This plasma etching technique is a dry etching technique. Specifically, a mask pattern is formed on a solid material as a workpiece through a resist. Next, in a state where this solid material is supported in a vacuum, a reactive gas is introduced into this vacuum, and a high-frequency electric field is applied to the reactive gas. As a result, accelerated electrons collide against gas molecules to be in a plasma state. Next, radicals (free radicals) produced from the plasma and ions are caused to react with the solid material so as to be removed as a reaction product. As a result, a fine pattern is formed on the solid material.
On the other hand, in a plasma CVD method which is a thin film forming technique, a compound, which is obtained by plasma causing raw material gases to combine with each other, is deposited on a substrate. In this method, a high-frequency electric field is applied to gases containing raw material molecules to discharge plasma. The raw material molecules are decomposed by electrons accelerated by the plasma discharge to obtain a compound, and the obtained compound is deposited on a substrate. A reaction, which does not occur only with thermal excitation at a low temperature, may occur in plasma because gases in the system collide against each other and are activated into radicals.
In a semiconductor manufacturing device using plasma such as a plasma etching device or a plasma CVD device, in the related art, an electrostatic chucking device is used as a device which simply attaches and fixes a wafer as a workpiece to a sample stage and maintains the wafer at a desired temperature.
This electrostatic chucking device includes: a substantially disk-shaped dielectric plate on which a wafer is placed; and an electrode for electrostatic adsorption that is embedded in the dielectric plate. By applying a direct current voltage between the dielectric plate and the wafer placed on the dielectric plate, an electrostatic adsorption force is generated due to the Coulomb force or a small leakage current. Due to this electrostatic adsorption force, the wafer is fixed to the dielectric plate.
As the dielectric plate used in the electrostatic chucking device, a ceramic such as aluminum oxide, aluminum nitride, or yttrium oxide is generally used.
As such an electrostatic chucking device, for example, an electrostatic chucking device is disclosed in which a base body of an electrostatic chuck includes a ceramic member which is formed of a yttrium oxide sintered body, the yttrium oxide sintered body including 5 vol % to 40 vol % of silicon nitride, and the ceramic member having a volume resistivity of 1×1015 Ω·cm or higher at room temperature and a relative dielectric constant of 10 or higher. As a result, high adsorption force and satisfactory desorption response of a workpiece are realized (Patent Citation 1).
In addition, in order to improve the yield and reliability of a chip in a semiconductor process, it is necessary to reduce an in-plane variation in the surface temperature of a wafer. Therefore, an electrostatic chuck is disclosed in which a semiconductor substrate such as a silicon wafer can be uniformly processed by using an aluminum nitride sintered body. In this aluminum nitride sintered body, when measured at plural measurement points including the center and an outer periphery of a surface of a wafer, an average relative density is 98% or higher, an average volume specific resistance value at 50° C. is 107 Ω·cm to 1012 Ω·cm, an average dielectric loss at a frequency of 1 MHz is 50×10−4 or lower, and a difference between a maximum dielectric loss value and a minimum dielectric loss value is 50% or lower of the average dielectric loss (Patent Citation 2).
On the other hand, as an electrostatic chuck in which the power of suppressing residual adsorption is not likely to deteriorate over time, an electrostatic chuck in which an insulating substrate formed of aluminum oxide or aluminum nitride is used is disclosed (Patent Citation 3).
In this electrostatic chuck, by controlling the dielectric loss of the material used for the insulating substrate to be 1×10−4 or lower, the temperature distribution on the surface of the insulating substrate is improved. As a result, non-uniformity in the surface temperature is improved.
[Patent Citation 1] Japanese Laid-open Patent Publication No. 2006-225185
[Patent Citation 2] Japanese Laid-open Patent Publication No. 2003-40674
[Patent Citation 3] Pamphlet of International Re-Publication No. WO2012/014873